1. Field of the Invention
The present invention relates to a high density data storage device using particle beam and its reading apparatus, in particular to a high density data storage device capable of improving storage density by storing each data at different position and height in the storage medium, a reading apparatus for high density data using particle beam and a system using these devices.
2. Description of the Prior Art
Efforts have been made up to present to reduce the area of storage by using microfilm to store and preserve documents. In the case of an ordinary microfilm, for instance, an A-4 size document (297 millimeter high and 210 millimeter wide) is stored by being reduced to about 1 centimeter. Reproduction of the document content becomes possible by enlarging the content of the microfilm. As a result, the area of document storage was reduced by over 1/600, improving the efficiency of document storage. With the increase in document items, however, this method has become insufficient and has led to the proposal for methods of high density data storage that are publicly known such as optical disk, magnetic disk and magneto-optical disk. Optical disk, for instance, stores data by irradiating narrowly focused laser beam to the storage medium and forming a small hole called a pit on the storage medium. Meanwhile, a method of reading the stored data by irradiating narrowly focused laser beam to the storage medium, as done at the time of data storage, and detecting reflection from the storage medium is used to read the data that has been stored. Since reducing the pit size will improve the density of storage, realization of pits about the size of approximately 1 .mu.m has led to expansion of the volume of data storage. In addition, the use of magnet or light for storage and reading of data in magnetic disks and magneto-optical disks has resulted in expansion of the volume of data storage through reduction of data storage unit as in optical disks.
A means for storing two different series of data on the same substrate by changing the pit depth to increase the volume of storage in an optical disk has been proposed as described, for instance, in Japanese Patent Application Laid Open No. 63-257921.
Moreover, a method using electron beams for data storage has also been proposed. For instance, as described in Japanese Patent Application Laid Open No. 2-195638, it is a method for storing the content of sample structure by irradiating an electron beam that permeated a sample to a two-dimensional sensor called a fluorescent recording sheet. The stored data is read by discharging light from the foregoing two-dimensional sensor through irradiation of light or heating. High-sensitivity storage of electron beam microscope image has become possible as a result.
Moreover, the development of a navigation system which is equipped with a storage medium for storing map data and with a means for detecting the current position of a mobile unit, and performs movement control of a mobile unit by comparing that map information with the current position of the mobile unit is recently under way for safe operation of mobile units, particularly for automobiles. Generally, map data is stored in an optical disk, and current position is judged by comparing with map data that has been stored by detecting radio wave from radio wave sources that are installed at various points on the street and from satellites.
Furthermore, an overhead projection method is already known as a method wherein characters and patterns are drawn on films made of plastic etc. and the foregoing characters and patterns are projected on a screen via magnification lens after transmitting visible radiation through it.
Another method already known is microfilm, which is a method wherein document data is photographed on a film and magnified via projection lens for reading.
The feature of these conventional technologies is that they read out the content of data stored on a storage medium, i.e. film, by projecting image through transmission of light through a film. These technologies are used in many areas because of their simple operation and small data storage space requirement.
Among the foregoing conventional technologies, however, optical disk, magnetic disk and magneto-optical disk have a problem of difficulty in reducing the minimum data storage unit to below 0.5 .mu.m. There is an additional problem of the limitations in improving data storage density at the time of storing data because the status of data storage is in two values (1 and 0). The foregoing publicly-known example of an optical disk is basically limited to storage of two value data. Moreover, there was a problem of difficulty in reading data at any location on a storage medium because data reading was performed sequentially.
Furthermore, the high sensitivity storage by electron beam microscope according to the foregoing conventional technology is not suitable for improving data storage density because the image stored on a two-dimensional sensor is a magnified image of a sample.